This invention relates to a film structure for flexible containers. In particular, this invention relates to a polyolefin film for steam sterilizable containers capable of containing a liquid to be maintained and accessed under sterile conditions.
Flexible, collapsible liquid containers are utilized in the medical industry for parenteral solutions and the like. Typically, these containers consist of a liquid containing body defined by heat sealed walls. Because these containers are utilized to contain fluids that are introduced intravenously into patients, it is necessary that the containers: are essentially transparent; are flexible; essentially free of extractables; and are sterilizable.
Various materials and structures have been utilized for parenteral solution containers. The materials that have been utilized include polyethylene, polyvinyl chloride, polypropylene, poly(ethylene methyl acrylate), and other copolymers.
One of the problems of the prior art film is that if these containers are to be steam sterilized, it is necessary that the outer layer of the film has a sufficiently high softening temperature so that it does not substantially deform during sterilization. In the prior art, creating a steam sterilizable outer layer usually resulted in sacrificing some other desired property. For example, to achieve the desired thermal resistance when a polyolefin is utilized, the thickness of the polyolefin has been increased to such an extent that clarity was impaired.
It has also been found that mechanical properties like impact strength decrease with an increase in the softening temperature of the polyolefin structure. Accordingly, if a polyolefin structure with a higher softening temperature is utilized, an increase in the thickness of the polyolefin film structure is required. This increase in thickness results in poor optical properties and a lack of flexibility that results in an increase in the size of the container. Moreover, because the flexible container is created by the inner surfaces of the polyolefin film being heat sealed together, the increase in thickness and/or softening temperature increases the time necessary for effectuating these seals. This in turn increases the duration of the production cycle necessary to create the flexible container, thereby resulting in a less economical flexible container.
Another example of a film structure that has not provided entirely satisfactory results is a polyethylene film structure. Because of polyethylene's susceptability to deformation, lower sterilization temperatures have been utilized for films constructed from polyethylene. The use of lower sterilization temperatures lengthens the total cycle duration for the production of flexible containers from polyethylene. This results in a less economical production cycle and accordingly a more expensive container.
Thus, there is a need for a new polyolefin film structure for creating steam sterilizable, flexible containers that overcomes the problems of the prior art.